Short-term treatment with rapamycin and dietary restriction have overlapping and distinctive effects in young mice

Does diet influence aging? Evidence from animal studies

Nutrition profoundly influences the risk for many age-related diseases. Whether nutrition influences human aging biology directly is less clear. Studies in different animal species indicate that reducing food intake ("caloric restriction" [CR]) can increase lifespan and delay the onset of diseases and the biological hallmarks of aging. Obesity has been described as "accelerated aging" and therefore the lifespan and health benefits generated by CR in both aging and obesity may occur via similar mechanisms. Beyond calorie intake, studies based on nutritional geometry have shown that protein intake and the interaction between dietary protein and carbohydrates influence age-related health and lifespan. Studies where animals are calorically restricted by providing free access to diluted diets have had less impact on lifespan than those studies where animals are given a reduced aliquot of food each day and are fasting between meals. This has drawn attention to the role of fasting in health and aging, and exploration of the health effects of various fasting regimes. Although definitive human clinical trials of nutrition and aging would need to be unfeasibly long and unrealistically controlled, there is good evidence from animal experiments that some nutritional interventions based on CR, manipulating dietary macronutrients, and fasting can influence aging biology and lifespan.

Combinatorial interventions in aging

Insight on the underlying mechanisms of aging will advance our ability to extend healthspan, treat age-related pathology and improve quality of life. Multiple genetic and pharmacological manipulations extend longevity in different species, yet monotherapy may be relatively inefficient, and we have limited data on the effect of combined interventions. Here we summarize interactions between age-related pathways and discuss strategies to simultaneously retard these in different organisms. In some cases, combined manipulations additively increase their impact on common hallmarks of aging and lifespan, suggesting they quantitatively participate within the same pathway. In other cases, interactions affect different hallmarks, suggesting their joint manipulation may independently maximize their effects on lifespan and healthy aging. While most interaction studies have been conducted with invertebrates and show varying levels of translatability, the conservation of pro-longevity pathways offers an opportunity to identify 'druggable' targets relevant to multiple human age-associated pathologies.

When a calorie is not just a calorie: Diet quality and timing as mediators of metabolism and healthy aging

An epidemic of obesity has affected large portions of the world, increasing the risk of developing many different age-associated diseases, including cancer, cardiovascular disease, and diabetes. In contrast with the prevailing notion that "a calorie is just a calorie," there are clear differences, within and between individuals, in the metabolic response to different macronutrient sources. Recent findings challenge this oversimplification; calories from different macronutrient sources or consumed at different times of day have metabolic effects beyond their value as fuel. Here, we summarize discussions conducted at a recent NIH workshop that brought together experts in calorie restriction, macronutrient composition, and time-restricted feeding to discuss how dietary composition and feeding schedule impact whole-body metabolism, longevity, and healthspan. These discussions may provide insights into the long-sought molecular mechanisms engaged by calorie restriction to extend lifespan, lead to novel therapies, and potentially inform the development of a personalized food-as-medicine approach to healthy aging.

Geroprotective interventions in the 3xTg mouse model of Alzheimer's disease

Alzheimer's disease (AD) is an age-associated neurodegenerative disease. As the population ages, the increasing prevalence of AD threatens massive healthcare costs in the coming decades. Unfortunately, traditional drug development efforts for AD have proven largely unsuccessful. A geroscience approach to AD suggests that since aging is the main driver of AD, targeting aging itself may be an effective way to prevent or treat AD. Here, we discuss the effectiveness of geroprotective interventions on AD pathology and cognition in the widely utilized triple-transgenic mouse model of AD (3xTg-AD) which develops both β-amyloid and tau pathologies characteristic of human AD, as well as cognitive deficits. We discuss the beneficial impacts of calorie restriction (CR), the gold standard for geroprotective interventions, and the effects of other dietary interventions including protein restriction. We also discuss the promising preclinical results of geroprotective pharmaceuticals, including rapamycin and medications for type 2 diabetes. Though these interventions and treatments have beneficial effects in the 3xTg-AD model, there is no guarantee that they will be as effective in humans, and we discuss the need to examine these interventions in additional animal models as well as the urgent need to test if some of these approaches can be translated from the lab to the bedside for the treatment of humans with AD.

Distinct and additive effects of calorie restriction and rapamycin in aging skeletal muscle

Preserving skeletal muscle function is essential to maintain life quality at high age. Calorie restriction (CR) potently extends health and lifespan, but is largely unachievable in humans, making “CR mimetics” of great interest. CR targets nutrient-sensing pathways centering on mTORC1. The mTORC1 inhibitor, rapamycin, is considered a potential CR mimetic and is proven to counteract age-related muscle loss. Therefore, we tested whether rapamycin acts via similar mechanisms as CR to slow muscle aging. Here we show that long-term CR and rapamycin unexpectedly display distinct gene expression profiles in geriatric mouse skeletal muscle, despite both benefiting aging muscles. Furthermore, CR improves muscle integrity in mice with nutrient-insensitive, sustained muscle mTORC1 activity and rapamycin provides additive benefits to CR in naturally aging mouse muscles. We conclude that rapamycin and CR exert distinct, compounding effects in aging skeletal muscle, thus opening the possibility of parallel interventions to counteract muscle aging.

The anti-aging intervention calorie restriction (CR) is thought to act via the nutrient-sensing multiprotein complex mTORC1. Here the authors show that the mTORC1-inhibitor rapamycin and CR use largely distinct mechanisms to slow mouse muscle aging.

Dietary Restriction and Rapamycin Affect Brain Aging in Mice by Attenuating Age-Related DNA Methylation Changes

The fact that dietary restriction (DR) and long-term rapamycin treatment (RALL) can ameliorate the aging process has been reported by many researchers. As the interface between external and genetic factors, epigenetic modification such as DNA methylation may have latent effects on the aging rate at the molecular level. To understand the mechanism behind the impacts of dietary restriction and rapamycin on aging, DNA methylation and gene expression changes were measured in the hippocampi of different-aged mice. Examining the single-base resolution of DNA methylation, we discovered that both dietary restriction and rapamycin treatment can maintain DNA methylation in a younger state compared to normal-aged mice. Through functional enrichment analysis of genes in which DNA methylation or gene expression can be affected by DR/RALL, we found that DR/RALL may retard aging through a relationship in which DNA methylation and gene expression work together not only in the same gene but also in the same biological process. This study is instructive for understanding the maintenance of DNA methylation by DR/RALL in the aging process, as well as the role of DR and RALL in the amelioration of aging.

Molecular mechanisms of dietary restriction promoting health and longevity

Dietary restriction with adequate nutrition is the gold standard for delaying ageing and extending healthspan and lifespan in diverse species, including rodents and non-human primates. In this Review, we discuss the effects of dietary restriction in these mammalian model organisms and discuss accumulating data that suggest that dietary restriction results in many of the same physiological, metabolic and molecular changes responsible for the prevention of multiple ageing-associated diseases in humans. We further discuss how different forms of fasting, protein restriction and specific reductions in the levels of essential amino acids such as methionine and the branched-chain amino acids selectively impact the activity of AKT, FOXO, mTOR, nicotinamide adenine dinucleotide (NAD⁺), AMP-activated protein kinase (AMPK) and fibroblast growth factor 21 (FGF21), which are key components of some of the most important nutrient-sensing geroprotective signalling pathways that promote healthy longevity.

Antiaging diets: Separating fact from fiction

[Figure: see text].

The autophagy inducer spermidine protects against metabolic dysfunction during overnutrition

Autophagy, a process catabolizing intracellular components to maintain energy homeostasis, impacts aging and metabolism. Spermidine, a natural polyamine and autophagy activator, extends lifespan across a variety of species, including mice. In addition to protecting cardiac and liver tissue, spermidine also affects adipose tissue through unexplored mechanisms. Here, we examined spermidine in the links between autophagy and systemic metabolism. Consistently, daily injection of spermidine delivered even at late life is sufficient to cause a trend in lifespan extension in wild type mice. We further found that spermidine has minimal metabolic effects in young and old mice under normal nutrition. However, spermidine counteracts HFD (high-fat diet)-induced obesity by increasing lipolysis in visceral fat. Mechanistically, spermidine increases the hepatokine FGF21 expression in liver without reducing food intake. Spermidine also modulates FGF21 in adipose tissues, elevating FGF21 expression in subcutaneous fat, but reducing it in visceral fat. Despite this, FGF21 is not required for spermidine action, since Fgf21  -/- mice were still protected from HFD. Furthermore, the enhanced lipolysis by spermidine was also independent of autophagy in adipose tissue, given that adipose-specific autophagy deficient (Beclin-1  flox/+  Fabp4-cre) mice remained spermidine-responsive under HFD. Our results suggest that the metabolic effects of spermidine occurs through systemic changes in metabolism, involving multiple mechanistic pathways.

Molecular Regulation of Skeletal Muscle Growth and Organelle Biosynthesis: Practical Recommendations for Exercise Training

The regulation of skeletal muscle mass and organelle homeostasis is dependent on the capacity of cells to produce proteins and to recycle cytosolic portions. In this investigation, the mechanisms involved in skeletal muscle mass regulation-especially those associated with proteosynthesis and with the production of new organelles-are presented. Thus, the critical roles of mammalian/mechanistic target of rapamycin complex 1 (mTORC1) pathway and its regulators are reviewed. In addition, the importance of ribosome biogenesis, satellite cells involvement, myonuclear accretion, and some major epigenetic modifications related to protein synthesis are discussed. Furthermore, several studies conducted on the topic of exercise training have recognized the central role of both endurance and resistance exercise to reorganize sarcomeric proteins and to improve the capacity of cells to build efficient organelles. The molecular mechanisms underlying these adaptations to exercise training are presented throughout this review and practical recommendations for exercise prescription are provided. A better understanding of the aforementioned cellular pathways is essential for both healthy and sick people to avoid inefficient prescriptions and to improve muscle function with emergent strategies (e.g., hypoxic training). Finally, current limitations in the literature and further perspectives, notably on epigenetic mechanisms, are provided to encourage additional investigations on this topic.

TOR Signaling Pathway in Cardiac Aging and Heart Failure

Mechanistic Target of Rapamycin (mTOR) signaling is a key regulator of cellular metabolism, integrating nutrient sensing with cell growth. Over the past two decades, studies on the mTOR pathway have revealed that mTOR complex 1 controls life span, health span, and aging by modulating key cellular processes such as protein synthesis, autophagy, and mitochondrial function, mainly through its downstream substrates. Thus, the mTOR pathway regulates both physiological and pathological processes in the heart from embryonic cardiovascular development to maintenance of cardiac homeostasis in postnatal life. In this regard, the dysregulation of mTOR signaling has been linked to many age-related pathologies, including heart failure and age-related cardiac dysfunction. In this review, we highlight recent advances of the impact of mTOR complex 1 pathway and its regulators on aging and, more specifically, cardiac aging and heart failure.

Targeting cellular senescence based on interorganelle communication, multilevel proteostasis, and metabolic control

Cellular senescence, a stable cell division arrest caused by severe damage and stress, is a hallmark of aging in vertebrates including humans. With progressing age, senescent cells accumulate in a variety of mammalian tissues, where they contribute to tissue aging, identifying cellular senescence as a major target to delay or prevent aging. There is an increasing demand for the discovery of new classes of small molecules that would either avoid or postpone cellular senescence by selectively eliminating senescent cells from the body (i.e., ‘senolytics’) or inactivating/switching damage‐inducing properties of senescent cells (i.e., ‘senostatics/senomorphics’), such as the senescence‐associated secretory phenotype. Whereas compounds with senolytic or senostatic activity have already been described, their efficacy and specificity has not been fully established for clinical use yet. Here, we review mechanisms of senescence that are related to mitochondria and their interorganelle communication, and the involvement of proteostasis networks and metabolic control in the senescent phenotype. These cellular functions are associated with cellular senescence in in vitro and in vivo models but have not been fully exploited for the search of new compounds to counteract senescence yet. Therefore, we explore possibilities to target these mechanisms as new opportunities to selectively eliminate and/or disable senescent cells with the aim of tissue rejuvenation. We assume that this research will provide new compounds from the chemical space which act as mimetics of caloric restriction, modulators of calcium signaling and mitochondrial physiology, or as proteostasis optimizers, bearing the potential to counteract cellular senescence, thereby allowing healthy aging.

Still Living Better through Chemistry: An Update on Caloric Restriction and Caloric Restriction Mimetics as Tools to Promote Health and Lifespan

Caloric restriction (CR), the reduction of caloric intake without inducing malnutrition, is the most reproducible method of extending health and lifespan across numerous organisms, including humans. However, with nearly one-third of the world’s population overweight, it is obvious that caloric restriction approaches are difficult for individuals to achieve. Therefore, identifying compounds that mimic CR is desirable to promote longer, healthier lifespans without the rigors of restricting diet. Many compounds, such as rapamycin (and its derivatives), metformin, or other naturally occurring products in our diets (nutraceuticals), induce CR-like states in laboratory models. An alternative to CR is the removal of specific elements (such as individual amino acids) from the diet. Despite our increasing knowledge of the multitude of CR approaches and CR mimetics, the extent to which these strategies overlap mechanistically remains unclear. Here we provide an update of CR and CR mimetic research, summarizing mechanisms by which these strategies influence genome function required to treat age-related pathologies and identify the molecular fountain of youth.

Rapamycin-mediated mouse lifespan extension: Late-life dosage regimes with sex-specific effects

To see if variations in timing of rapamycin (Rapa), administered to middle aged mice starting at 20 months, would lead to different survival outcomes, we compared three dosing regimens. Initiation of Rapa at 42 ppm increased survival significantly in both male and female mice. Exposure to Rapa for a 3‐month period led to significant longevity benefit in males only. Protocols in which each month of Rapa treatment was followed by a month without Rapa exposure were also effective in both sexes, though this approach was less effective than continuous exposure in female mice. Interpretation of these results is made more complicated by unanticipated variation in patterns of weight gain, prior to the initiation of the Rapa treatment, presumably due to the use of drug‐free food from two different suppliers. The experimental design included tests of four other drugs, minocycline, β‐guanidinopropionic acid, MitoQ, and 17‐dimethylaminoethylamino‐17‐demethoxygeldanamycin (17‐DMAG), but none of these led to a change in survival in either sex.

Is Rapamycin a Dietary Restriction Mimetic?

Since the initial suggestion that rapamycin, an inhibitor of target of rapamycin (TOR) nutrient signaling, increased lifespan comparable to dietary restriction, investigators have viewed rapamycin as a potential dietary restriction mimetic. Both dietary restriction and rapamycin increase lifespan across a wide range of evolutionarily diverse species (including yeast, Caenorhabditis elegans, Drosophila, and mice) as well as reducing pathology and improving physiological functions that decline with age in mice. The purpose of this article is to review the research comparing the effect of dietary restriction and rapamycin in mice. The current data show that dietary restriction and rapamycin have different effects on many pathways and molecular processes. In addition, these interventions affect the lifespan of many genetically manipulated mouse models differently. In other words, while dietary restriction and rapamycin may have similar effects on some pathways and processes; overall, they affect many pathways/processes quite differently. Therefore, rapamycin is likely not a true dietary restriction mimetic. Rather dietary restriction and rapamycin appear to be increasing lifespan and retarding aging largely through different mechanisms/pathways, suggesting that a combination of dietary restriction and rapamycin will have a greater effect on lifespan than either manipulation alone.

Life-span Extension Drug Interventions Affect Adipose Tissue Inflammation in Aging

The National Institute on Aging (NIA)-sponsored Interventions Testing Program (ITP) has identified a number of dietary drug interventions that significantly extend life span, including rapamycin, acarbose, and 17-α estradiol. However, these drugs have diverse downstream targets, and their effects on age-associated organ-specific changes are unclear (Nadon NL, Strong R, Miller RA, Harrison DE. NIA Interventions Testing Program: investigating putative aging intervention agents in a genetically heterogeneous mouse model. EBioMedicine. 2017;21:3-4. doi:10.1016/j.ebiom.2016.11.038). Potential mechanisms by which these drugs extend life could be through their effect on inflammatory processes often noted in tissues of aging mice and humans. Our study focuses on the effects of three drugs in the ITP on inflammation in gonadal white adipose tissue (gWAT) of HET3 mice-including adiposity, adipose tissue macrophage (ATM) M1/M2 polarization, markers of cellular senescence, and endoplasmic reticulum stress. We found that rapamycin led to a 56% increase of CD45+ leukocytes in gWAT, where the majority of these are ATMs. Interestingly, rapamycin led to a 217% and 106% increase of M1 (CD45+CD64+CD206-) ATMs in females and males, respectively. Our data suggest rapamycin may achieve life-span extension in part through adipose tissue inflammation. Additionally, HET3 mice exhibit a spectrum of age-associated changes in the gWAT, but acarbose and 17-α estradiol do not strongly alter these phenotypes-suggesting that acarbose and 17- α estradiol may not influence life span through mechanisms involving adipose tissue inflammation.

Differential Effects of Rapamycin on Glucose Metabolism in Nine Inbred Strains

Studies in mice suggest that rapamycin has a negative impact on glucose homeostasis by inducing insulin resistance. However, results have been inconsistent and difficult to assess because the strains, methods of treatment, and analysis vary among studies. Using a consistent protocol, we surveyed nine inbred strains of mice for the effect of rapamycin on various aspects of glucose metabolism. Across all strains, rapamycin significantly delayed glucose clearance after challenge. However, rapamycin showed no main effect on systemic insulin sensitivity. Analysis of individual strains shows that rapamycin induced higher glucose values at 15 minutes post-challenge in 7/9 strains. However, only three strains show rapamycin-induced reduction in glucose clearance from 15 to 120 minutes. Although pancreatic insulin content was reduced by rapamycin in seven strains, none showed reduced serum insulin values. Although one strain showed no effects of rapamycin on glucose metabolism (129), another showed increased systemic insulin sensitivity (B6). We suggest that rapamycin likely inhibits insulin production and secretion in most strains while having strain-specific effects on glucose clearance without altering systemic insulin sensitivity. This strain survey indicates that genetic differences greatly influence the metabolic response to rapamycin.

Rapamycin for longevity: opinion article

From the dawn of civilization, humanity has dreamed of immortality. So why didn't the discovery of the anti-aging properties of mTOR inhibitors change the world forever? I will discuss several reasons, including fear of the actual and fictional side effects of rapamycin, everolimus and other clinically-approved drugs, arguing that no real side effects preclude their use as anti-aging drugs today. Furthermore, the alternative to the reversible (and avoidable) side effects of rapamycin/everolimus are the irreversible (and inevitable) effects of aging: cancer, stroke, infarction, blindness and premature death. I will also discuss why it is more dangerous not to use anti-aging drugs than to use them and how rapamycin-based drug combinations have already been implemented for potential life extension in humans. If you read this article from the very beginning to its end, you may realize that the time is now.

Role of mTORC1 in mechanically induced increases in translation and skeletal muscle mass

Skeletal muscle mass is, in part, regulated by the rate of mRNA translation (i.e., protein synthesis). The conserved serine/threonine kinase, mTOR (the mammalian/mechanistic target of rapamycin), found in the multiprotein complex, mTOR complex 1 (mTORC1), is a major positive regulator of protein synthesis. The purpose of this review is to describe some of the critical steps in translation initiation, mTORC1 and its potential direct and indirect roles in regulating translation, and evidence that mTORC1 regulates protein synthesis and muscle mass, with a particular focus on basal conditions and the response to mechanical stimuli. Current evidence suggests that for acute contraction models of mechanical stimuli, there is an emerging pattern suggesting that there is an early increase in protein synthesis governed by a rapamycin-sensitive mTORC1-dependent mechanism, while at later poststimulation time points, the mechanism may change to a rapamycin-insensitive mTORC1-dependent or even an mTORC1-independent mechanism. Furthermore, evidence suggests that mTORC1 appears to be absolutely necessary for muscle fiber hypertrophy induced by chronic mechanical loading but may only play a partial role in the hypertrophy induced by more intermittent types of acute resistance exercise, with the possibility of mTORC1-independent mechanisms also playing a role. Despite the progress that has been made, many questions about the activation of mTORC1, and its downstream targets, remain to be answered. Further research will hopefully provide novel insights into the regulation of skeletal muscle mTORC1 that may eventually be translated into novel exercise programing and/or targeted pharmacological therapies aimed at preventing muscle wasting and/or increasing muscle mass.

Effects of food restriction on the expression of genes related to acetaminophen-induced liver toxicity in rats

It is well known that fasting substantially affects the metabolism of drugs and chemicals. Food restriction also affects drug kinetics, such as absorption, metabolism, and excretion, and therefore, it can potentially modulate the onset of chemical toxicity or drug-induced adverse reactions. In the present study, the expression of drug-metabolizing enzyme genes and total glutathione content in the liver, which are related to toxicity induced by overdose of the hepatotoxic drug acetaminophen (N-acetyl-p-aminophenol; APAP), were examined in rats reared under different feeding conditions: ad libitum feeding, 16-h fasting, and food restriction (fed 70% of the average intake of ad libitum feeding for 10 days) conditions. The rats under food restriction conditions as well as fasted rats showed significantly higher expression of Cyp2e1, the gene encoding the enzyme that metabolizes APAP to its toxic metabolite N-acetyl-p-benzoquinone imine (NAPQI). They also had lower levels of liver total glutathione, which detoxifies NAPQI. In contrast, the gene expression of UDP-glucuronosyltransferase 1A6 (Ugt1a6), sulfotransferase 1A1 (Sult1a1), and glutathione S-transferase M1 (Gstm1) was not affected by food restriction or fasting. When APAP was administered (800 mg/kg), histopathological changes were not observed in rats fed ad libitum, while hepatocellular necrosis was observed in most of the rats treated with APAP after fasting or food restriction. Taken together, these results suggest that not only fasting but also food restriction exacerbate APAP-induced acute liver injury, probably by the induction of CYP2E1 and the reduction of liver glutathione contents, in rodents.

From rapalogs to anti-aging formula

Inhibitors of mTOR, including clinically available rapalogs such as rapamycin (Sirolimus) and Everolimus, are gerosuppressants, which suppress cellular senescence. Rapamycin slows aging and extends life span in a variety of species from worm to mammals. Rapalogs can prevent age-related diseases, including cancer, atherosclerosis, obesity, neurodegeneration and retinopathy and potentially rejuvenate stem cells, immunity and metabolism. Here, I further suggest how rapamycin can be combined with metformin, inhibitors of angiotensin II signaling (Losartan, Lisinopril), statins (simvastatin, atorvastatin), propranolol, aspirin and a PDE5 inhibitor. Rational combinations of these drugs with physical exercise and an anti-aging diet (Koschei formula) can maximize their anti-aging effects and decrease side effects.

Caloric Restriction and Rapamycin Differentially Alter Energy Metabolism in Yeast

Rapamycin (RM), a drug that inhibits the mechanistic target of rapamycin (mTOR) pathway and responds to nutrient availability, seemingly mimics the effects of caloric restriction (CR) on healthy life span. However, the extent of the mechanistic overlap between RM and CR remains incompletely understood. Here, we compared the impact of CR and RM on cellular metabolic status. Both regimens maintained intracellular ATP through the chronological aging process and showed enhanced mitochondrial capacity. Comparative transcriptome analysis showed that CR had a stronger impact on global gene expression than RM. We observed a like impact on the metabolome and identified distinct metabolites affected by CR and RM. CR severely reduced the level of energy storage molecules including glycogen and lipid droplets, whereas RM did not. RM boosted the production of enzymes responsible for the breakdown of glycogen and lipid droplets. Collectively, these results provide insights into the distinct energy metabolism mechanisms induced by CR and RM, suggesting that these two anti-aging regimens might extend life span through distinctive pathways.

Beneficial effects of dietary restriction in aging brain

Aging is a multifactorial complex process that leads to the deterioration of biological functions wherein its underlying mechanism is not fully elucidated. It affects the organism at the molecular and cellular level that contributes to the deterioration of structural integrity of the organs. The central nervous system is the most vulnerable organ affected by aging and its effect is highly heterogeneous. Aging causes alteration in the structure, metabolism and physiology of the brain leading to impaired cognitive and motor-neural functions. Dietary restriction (DR), a robust mechanism that extends lifespan in various organisms, ameliorates brain aging by reducing oxidative stress, improving mitochondrial function, activating anti-inflammatory responses, promoting neurogenesis and increasing synaptic plasticity. It also protects and prevents age-related structural changes. DR alleviates many age-associated diseases including neurodegeneration and improves cognitive functions. DR inhibits/activates nutrient signaling cascades such as insulin/IGF-1, mTOR, AMPK and sirtuins. Because of its sensitivity to energy status and hormones, AMPK is considered as the global nutrient sensor. This review will present an elucidative potential role of dietary restriction in the prevention of phenotypic features during aging in brain and its diverse mechanisms.

Decreased mTOR signalling reduces mitochondrial ROS in brain via accumulation of the telomerase protein TERT within mitochondria

Telomerase in its canonical function maintains telomeres in dividing cells. In addition, the telomerase protein TERT has non-telomeric functions such as shuttling to mitochondria resulting in a decreased oxidative stress, DNA damage and apoptosis. TERT protein persists in adult neurons and can co-localise to mitochondria under various stress conditions. We show here that TERT expression decreased in mouse brain during aging while release of reactive oxygen species (ROS) from the mitochondrial electron transport chain increased. Dietary restriction (DR) caused accumulation of TERT protein in mouse brain mitochondria correlating to decreased ROS release and improved learning and spatial short-term memory. Decreased mTOR signalling is a mediator of DR. Accordingly, feeding mice with rapamycin increased brain mitochondrial TERT and reduced ROS release. Importantly, the beneficial effects of rapamycin on mitochondrial function were absent in brains and fibroblasts from first generation TERT -/- mice, and when TERT shuttling was inhibited by the Src kinase inhibitor bosutinib. Taken together, our data suggests that the mTOR signalling pathway impinges on the mitochondrial localisation of TERT protein, which might in turn contribute to the protection of the brain by DR or rapamycin against age-associated mitochondrial ROS increase and cognitive decline.

Comparative idiosyncrasies in life extension by reduced mTOR signalling and its distinctiveness from dietary restriction

Reduced mechanistic target of rapamycin (mTOR) signalling extends lifespan in yeast, nematodes, fruit flies and mice, highlighting a physiological pathway that could modulate aging in evolutionarily divergent organisms. This signalling system is also hypothesized to play a central role in lifespan extension via dietary restriction. By collating data from 48 available published studies examining lifespan with reduced mTOR signalling, we show that reduced mTOR signalling provides similar increases in median lifespan across species, with genetic mTOR manipulations consistently providing greater life extension than pharmacological treatment with rapamycin. In contrast to the consistency in changes in median lifespan, however, the demographic causes for life extension are highly species specific. Reduced mTOR signalling extends lifespan in nematodes by strongly reducing the degree to which mortality rates increase with age (aging rate). By contrast, life extension in mice and yeast occurs largely by pushing back the onset of aging, but not altering the shape of the mortality curve once aging starts. Importantly, in mice, the altered pattern of mortality induced by reduced mTOR signalling is different to that induced by dietary restriction, which reduces the rate of aging. Effects of mTOR signalling were also sex dependent, but only within mice, and not within flies, thus again species specific. An alleviation of age‐associated mortality is not a shared feature of reduced mTOR signalling across model organisms and does not replicate the established age‐related survival benefits of dietary restriction.

DNA Damage: A Main Determinant of Vascular Aging

Vascular aging plays a central role in health problems and mortality in older people. Apart from the impact of several classical cardiovascular risk factors on the vasculature, chronological aging remains the single most important determinant of cardiovascular problems. The causative mechanisms by which chronological aging mediates its impact, independently from classical risk factors, remain to be elucidated. In recent years evidence has accumulated that unrepaired DNA damage may play an important role. Observations in animal models and in humans indicate that under conditions during which DNA damage accumulates in an accelerated rate, functional decline of the vasculature takes place in a similar but more rapid or more exaggerated way than occurs in the absence of such conditions. Also epidemiological studies suggest a relationship between DNA maintenance and age-related cardiovascular disease. Accordingly, mouse models of defective DNA repair are means to study the mechanisms involved in biological aging of the vasculature. We here review the evidence of the role of DNA damage in vascular aging, and present mechanisms by which genomic instability interferes with regulation of the vascular tone. In addition, we present potential remedies against vascular aging induced by genomic instability. Central to this review is the role of diverse types of DNA damage (telomeric, non-telomeric and mitochondrial), of cellular changes (apoptosis, senescence, autophagy), mediators of senescence and cell growth (plasminogen activator inhibitor-1 (PAI-1), cyclin-dependent kinase inhibitors, senescence-associated secretory phenotype (SASP)/senescence-messaging secretome (SMS), insulin and insulin-like growth factor 1 (IGF-1) signaling), the adenosine monophosphate-activated protein kinase (AMPK)-mammalian target of rapamycin (mTOR)-nuclear factor kappa B (NFκB) axis, reactive oxygen species (ROS) vs. endothelial nitric oxide synthase (eNOS)-cyclic guanosine monophosphate (cGMP) signaling, phosphodiesterase (PDE) 1 and 5, transcription factor NF-E2-related factor-2 (Nrf2), and diet restriction.

Reduced in vivo hepatic proteome replacement rates but not cell proliferation rates predict maximum lifespan extension in mice

Combating the social and economic consequences of a growing elderly population will require the identification of interventions that slow the development of age-related diseases. Preserved cellular homeostasis and delayed aging have been previously linked to reduced cell proliferation and protein synthesis rates. To determine whether changes in these processes may contribute to or predict delayed aging in mammals, we measured cell proliferation rates and the synthesis and replacement rates (RRs) of over a hundred hepatic proteins in vivo in three different mouse models of extended maximum lifespan (maxLS): Snell Dwarf, calorie-restricted (CR), and rapamycin (Rapa)-treated mice. Cell proliferation rates were not consistently reduced across the models. In contrast, reduced hepatic protein RRs (longer half-lives) were observed in all three models compared to controls. Intriguingly, the degree of mean hepatic protein RR reduction was significantly correlated with the degree of maxLS extension across the models and across different Rapa doses. Absolute rates of hepatic protein synthesis were reduced in Snell Dwarf and CR, but not Rapa-treated mice. Hepatic chaperone levels were unchanged or reduced and glutathione S-transferase synthesis was preserved or increased in all three models, suggesting a reduced demand for protein renewal, possibly due to reduced levels of unfolded or damaged proteins. These data demonstrate that maxLS extension in mammals is associated with improved hepatic proteome homeostasis, as reflected by a reduced demand for protein renewal, and that reduced hepatic protein RRs hold promise as an early biomarker and potential target for interventions that delay aging in mammals.

Six-month Calorie Restriction in Overweight Individuals Elicits Transcriptomic Response in Subcutaneous Adipose Tissue That is Distinct From Effects of Energy Deficit

Calorie restriction confers health benefits distinct from energy deficit by exercise. We characterized the adipose-transcriptome to investigate the molecular basis of the differential phenotypic responses. Abdominal subcutaneous fat was collected from 24 overweight participants randomized in three groups (N = 8/group): weight maintenance (control), 25% energy deficit by calorie restriction alone (CR), and 25% energy deficit by calorie restriction with structured exercise (CREX). Within each group, gene expression was compared between 6 months and baseline with cutoffs at nominal p ≤ .01 and absolute fold-change ≥ 1.5. Gene-set enrichment analysis (false discovery rate < 5%) was used to identify significantly regulated biological pathways. CR and CREX elicited similar overall clinical response to energy deficit and a comparable reduction in gene transcription specific to oxidative phosphorylation and proteasome function. CR vastly outweighed CREX in the number of differentially regulated genes (88 vs 39) and pathways (28 vs 6). CR specifically downregulated the chemokine signaling-related pathways. Among the CR-regulated genes, 27 functioned as transcription/translation regulators (eg, mRNA processing or transcription/translation initiation), whereas CREX regulated only one gene in this category. Our data suggest that CR has a broader effect on the transcriptome compared with CREX which may mediate its specific impact on delaying primary aging.

Moderate calorie restriction to achieve normal weight reverses β-cell dysfunction in diet-induced obese mice: involvement of autophagy

Background

Severe calorie restriction (CR) is shown to improve or even reverse β-cell dysfunction in patients with obesity and type 2 diabetes mellitus. However, whether mild to moderate CR can reverse β-cell dysfunction induced by obesity and the underlying mechanism remain unclear. Autophagy plays an important role in maintaining mass, architecture and function of β-cells. While the impact of CR on β-cell autophagy is unknown. This study aims to investigate the effects of moderate CR on β-cell function and autophagy activity in diet-induced obese (DIO) mice.

Methods

DIO C57BL/6 mice were subjected to 3 weeks of switching to normal chow (HF → NC group) or normal chow with 40 % CR (HF → NC CR group). Then hematoxylin-eosin and immunohistochemistry staining were performed to observe β-cell morphology. β-cell function was evaluated by intraperitoneal glucose tolerance test in vivo and static GSIS (glucose-stimulated insulin secretion) in isolated islets. β-cell autophagy activity was determined by transmission electron microscope and western blot.

Results

In the HF → NC CR group, CR normalized body weights, completely restored glucose tolerance, early-phase and second-phase insulin secretion, insulin sensitivity, and islet size. CR also normalized insulin content and glucose-stimulated insulin secretion in isolated islets in vitro. Furthermore, β-cell autophagy level was increased in the HF → NC CR group, but AMPK phosphorylation remained unchanged. Although HF → NC mice achieved moderate weight loss and normal glucose tolerance, their insulin secretion was not improved compared with obese control mice, and additionally, β-cell autophagy was not activated in these mice.

Conclusions

Moderate (40 %) CR to achieve normal weight reversed β-cell dysfunction and insulin resistance, and restored glucose homeostasis in DIO mice. Furthermore, the up-regulation of β-cell autophagy may play a role in this process, independent of AMPK activation.

de Bruin R, N. M. Ijzermans J, van Kooten C, Dor FJMF. Mannan-Binding Lectin Is Involved in the Protection against Renal Ischemia/Reperfusion Injury by Dietary Restriction

Preoperative fasting and dietary restriction offer robust protection against renal ischemia/reperfusion injury (I/RI) in mice. We recently showed that Mannan-binding lectin (MBL), the initiator of the lectin pathway of complement activation, plays a pivotal role in renal I/RI. Based on these findings, we investigated the effect of short-term DR (30% reduction of total food intake) or three days of water only fasting on MBL in 10-12 weeks old male C57/Bl6 mice. Both dietary regimens significantly reduce the circulating levels of MBL as well as its mRNA expression in liver, the sole production site of MBL. Reconstitution of MBL abolished the protection afforded by dietary restriction, whereas in the fasting group the protection persisted. These data show that modulation of MBL is involved in the protection against renal I/RI induced by dietary restriction, and suggest that the mechanisms of protection induced by dietary restriction and fasting may be different.

Rapamycin-induced metabolic defects are reversible in both lean and obese mice

The inhibition of mTOR (mechanistic target of rapamycin) by the macrolide rapamycin has many beneficial effects in mice, including extension of lifespan and reduction or prevention of several age-related diseases. At the same time, chronic rapamycin treatment causes impairments in glucose metabolism including hyperglycemia, glucose intolerance and insulin resistance. It is unknown whether these metabolic effects of rapamycin are permanent or whether they can be alleviated. Here, we confirmed that rapamycin causes glucose intolerance and insulin resistance in both inbred and genetically heterogeneous mice fed either low fat or high fat diets, suggesting that these effects of rapamycin are independent of genetic background. Importantly, we also found that these effects were almost completely lost within a few weeks of cessation of treatment, showing that chronic rapamycin treatment does not induce permanent impairment of glucose metabolism. Somewhat surprisingly, chronic rapamycin also promoted increased accumulation of adipose tissue in high fat fed mice. However, this effect too was lost when rapamycin treatment was ended suggesting that this effect of rapamycin is also not permanent. The reversible nature of rapamycin's alterations of metabolic function suggests that these potentially detrimental side-effects might be managed through alternative dosing strategies or concurrent treatment options.

Angiotensin II blockade: how its molecular targets may signal to mitochondria and slow aging. Coincidences with calorie restriction and mTOR inhibition

Caloric restriction (CR), renin angiotensin system blockade (RAS-bl), and rapamycin-mediated mechanistic target of rapamycin (mTOR) inhibition increase survival and retard aging across species. Previously, we have summarized CR and RAS-bl's converging effects, and the mitochondrial function changes associated with their physiological benefits. mTOR inhibition and enhanced sirtuin and KLOTHO signaling contribute to the benefits of CR in aging. mTORC1/mTORC2 complexes contribute to cell growth and metabolic regulation. Prolonged mTORC1 activation may lead to age-related disease progression; thus, rapamycin-mediated mTOR inhibition and CR may extend lifespan and retard aging through mTORC1 interference. Sirtuins by deacetylating histone and transcription-related proteins modulate signaling and survival pathways and mitochondrial functioning. CR regulates several mammalian sirtuins favoring their role in aging regulation. KLOTHO/fibroblast growth factor 23 (FGF23) contribute to control Ca(2+), phosphate, and vitamin D metabolism, and their dysregulation may participate in age-related disease. Here we review how mTOR inhibition extends lifespan, how KLOTHO functions as an aging suppressor, how sirtuins mediate longevity, how vitamin D loss may contribute to age-related disease, and how they relate to mitochondrial function. Also, we discuss how RAS-bl downregulates mTOR and upregulates KLOTHO, sirtuin, and vitamin D receptor expression, suggesting that at least some of RAS-bl benefits in aging are mediated through the modulation of mTOR, KLOTHO, and sirtuin expression and vitamin D signaling, paralleling CR actions in age retardation. Concluding, the available evidence endorses the idea that RAS-bl is among the interventions that may turn out to provide relief to the spreading issue of age-associated chronic disease.

Gene expression in the liver of female, but not male mice treated with rapamycin resembles changes observed under dietary restriction

It is well known that in mice the extension in lifespan by rapamycin is sexually dimorphic, in that it has a larger effect in females than males. In a previous study we showed that in male C57BL6 mice, rapamycin had less profound effects in both gene expression and liver metabolites when compared to dietary restriction (DR), but no data was available in females. Because recent studies showed that rapamycin increases longevity in a dose dependent manner and at every dose tested the effect remains larger in females than in males, we hypothesized that rapamycin should have a stronger effect on gene expression in females, and this effect could be dose dependent. To test this hypothesis, we measured the changes in liver gene expression induced by rapamycin (14 ppm) with a focus on several genes involved in pathways known to play a role in aging and that are altered by DR. To investigate whether any effects are dose dependent, we also analyzed females treated with two additional doses of rapamycin (22 and 42 ppm). We observed striking differences between male and female in gene expression at 14 ppm, where females have a larger response to rapamycin than males, and the effects of rapamycin in females resemble what we observed under DR. However, these effects were generally not dose dependent. These data support the notion that female mice respond better to rapamycin, and at least with the set of genes studied here, the effect of rapamycin in females resemble the effect of DR.

Effect of age on basal muscle protein synthesis and mTORC1 signaling in a large cohort of young and older men and women

The rate of muscle loss with aging is higher in men than women. However, women have smaller muscles throughout the adult life. Protein content is a major determinant of skeletal muscle size. This study was designed to determine if age and sex differentially impact basal muscle protein synthesis and mammalian/mechanistic target of rapamycin complex 1 (mTORC1) signaling. We performed a secondary data analysis on a cohort of 215 healthy, non-obese (BMI<30kg·m(-2)) young (18-40y; 74 men, 52 women) and older (60-87y; 57 men, 32 women) adults. The database contained information on physical characteristics, basal muscle protein fractional synthetic rate (FSR; n=215; stable isotope methodology) and mTORC1 signaling (n=125, Western blotting). FSR and mTORC1 signaling were measured at rest and after an overnight fast. mTORC1 and S6K1 phosphorylation were higher (p<0.05) in older subjects with no sex differences. However, there were no age or sex differences or interaction for muscle FSR (p>0.05). Body mass index, fat free mass, or body fat was not a significant covariate and did not influence the results. We conclude that age and sex do not influence basal muscle protein synthesis. However, basal mTORC1 hyperphosphorylation in the elderly may contribute to insulin resistance and the age-related anabolic resistance of skeletal muscle protein metabolism to nutrition and exercise.

NaDC3 Induces Premature Cellular Senescence by Promoting Transport of Krebs Cycle Intermediates, Increasing NADH, and Exacerbating Oxidative Damage

High-affinity sodium-dependent dicarboxylate cotransporter 3 (NaDC3) is a key metabolism-regulating membrane protein responsible for transport of Krebs cycle intermediates. NaDC3 is upregulated as organs age, but knowledge regarding the underlying mechanisms by which NaDC3 modulates mammalian aging is limited. In this study, we showed that NaDC3 overexpression accelerated cellular senescence in young human diploid cells (MRC-5 and WI-38) and primary renal tubular cells, leading to cell cycle arrest in G1 phase and increased expression of senescent biomarkers, senescence-associated β-galactosidase and p16. Intracellular levels of reactive oxygen species, 8-hydroxy-2'-deoxyguanosine, malondialdehyde, and carbonyl were significantly enhanced, and activities of respiratory complexes I and III and ATP level were significantly decreased in NaDC3-infected cells. Stressful premature senescent phenotypes induced by NaDC3 were markedly ameliorated via treatment with the antioxidants Tiron and Tempol. High expression of NaDC3 caused a prominent increase in intracellular levels of Krebs cycle intermediates and NADH. Exogenous NADH and NAD(+) may aggravate and attenuate the aging phenotypes induced by NaDC3, respectively. These results suggest that NaDC3 can induce premature cellular senescence by promoting the transport of Krebs cycle intermediates, increasing generation of NADH and reactive oxygen species and leading to oxidative damage. Our results clarify the aging signaling pathway regulated by NaDC3.

Short-term rapamycin treatment in mice has few effects on the transcriptome of white adipose tissue compared to dietary restriction

Rapamycin, a drug that has been shown to increase lifespan in mice, inhibits the target of rapamycin (TOR) pathway, a major pathway that regulates cell growth and energy status. It has been hypothesized that rapamycin and dietary restriction (DR) extend lifespan through similar mechanisms/pathways. Using microarray analysis, we compared the transcriptome of white adipose tissue from mice fed rapamycin or DR-diet for 6 months. Multidimensional scaling and heatmap analyses showed that rapamycin had essentially no effect on the transcriptome as compared to DR. For example, only six transcripts were significantly altered by rapamycin while mice fed DR showed a significant change in over 1000 transcripts. Using ingenuity pathway analysis, we found that stearate biosynthesis and circadian rhythm signaling were significantly changed by DR. Our findings showing that DR, but not rapamycin, has an effect on the transcriptome of the adipose tissue, suggesting that these two manipulations increase lifespan through different mechanisms/pathways.

Rapamycin-mediated lifespan increase in mice is dose and sex dependent and metabolically distinct from dietary restriction

Rapamycin, an inhibitor of mTOR kinase, increased median lifespan of genetically heterogeneous mice by 23% (males) to 26% (females) when tested at a dose threefold higher than that used in our previous studies; maximal longevity was also increased in both sexes. Rapamycin increased lifespan more in females than in males at each dose evaluated, perhaps reflecting sexual dimorphism in blood levels of this drug. Some of the endocrine and metabolic changes seen in diet-restricted mice are not seen in mice exposed to rapamycin, and the pattern of expression of hepatic genes involved in xenobiotic metabolism is also quite distinct in rapamycin-treated and diet-restricted mice, suggesting that these two interventions for extending mouse lifespan differ in many respects.

Rapamycin and dietary restriction induce metabolically distinctive changes in mouse liver

Dietary restriction (DR) is the gold standard intervention used to delay aging, and much recent research has focused on the identification of possible DR mimetics. Energy sensing pathways, including insulin/IGF1 signaling, sirtuins, and mammalian Target of Rapamycin (mTOR), have been proposed as pathways involved in the antiaging actions of DR, and compounds that affect these pathways have been suggested to act as DR mimetics, including metformin (insulin/IGF1 signaling), resveratrol (sirtuins), and rapamycin (mTOR). Rapamycin is a promising DR mimetic because it significantly increases both health span and life span in mice. Unfortunately, rapamycin also leads to some negative effects, foremost among which is the induction of insulin resistance, potentially limiting its translation into humans. To begin clarifying the mechanism(s) involved in insulin resistance induced by rapamycin, we compared several aspects of liver metabolism in mice treated with DR or rapamycin for 6 months. Our data suggest that although both DR and rapamycin inhibit lipogenesis, activate lipolysis, and increased serum levels of nonesterified fatty acids, only DR further activates β-oxidation of the fatty acids leading to the production of ketone bodies.

Combined treatment of rapamycin and dietary restriction has a larger effect on the transcriptome and metabolome of liver

Rapamycin (Rapa) and dietary restriction (DR) have consistently been shown to increase lifespan. To investigate whether Rapa and DR affect similar pathways in mice, we compared the effects of feeding mice ad libitum (AL), Rapa, DR, or a combination of Rapa and DR (Rapa + DR) on the transcriptome and metabolome of the liver. The principal component analysis shows that Rapa and DR are distinct groups. Over 2500 genes are significantly changed with either Rapa or DR when compared with mice fed AL; more than 80% are unique to DR or Rapa. A similar observation was made when genes were grouped into pathways; two-thirds of the pathways were uniquely changed by DR or Rapa. The metabolome shows an even greater difference between Rapa and DR; no metabolites in Rapa-treated mice were changed significantly from AL mice, whereas 173 metabolites were changed in the DR mice. Interestingly, the number of genes significantly changed by Rapa + DR when compared with AL is twice as large as the number of genes significantly altered by either DR or Rapa alone. In summary, the global effects of DR or Rapa on the liver are quite different and a combination of Rapa and DR results in alterations in a large number of genes and metabolites that are not significantly changed by either manipulation alone, suggesting that a combination of DR and Rapa would be more effective in extending longevity than either treatment alone.

Mice fed rapamycin have an increase in lifespan associated with major changes in the liver transcriptome

Rapamycin was found to increase (11% to 16%) the lifespan of male and female C57BL/6J mice most likely by reducing the increase in the hazard for mortality (i.e., the rate of aging) term in the Gompertz mortality analysis. To identify the pathways that could be responsible for rapamycin's longevity effect, we analyzed the transcriptome of liver from 25-month-old male and female mice fed rapamycin starting at 4 months of age. Few changes (<300 transcripts) were observed in transcriptome of rapamycin-fed males; however, a large number of transcripts (>4,500) changed significantly in females. Using multidimensional scaling and heatmap analyses, the male mice fed rapamycin were found to segregate into two groups: one group that is almost identical to control males (Rapa-1) and a second group (Rapa-2) that shows a change in gene expression (>4,000 transcripts) with more than 60% of the genes shared with female mice fed Rapa. Using ingenuity pathway analysis, 13 pathways were significantly altered in both Rapa-2 males and rapamycin-fed females with mitochondrial function as the most significantly changed pathway. Our findings show that rapamycin has a major effect on the transcriptome and point to several pathways that would likely impact the longevity.

Calorie restriction alleviates the age-related decrease in neural progenitor cell division in the aging brain

Production of new neurons from stem cells is important for cognitive function, and the reduction of neurogenesis in the aging brain may contribute to the accumulation of age-related cognitive deficits. Restriction of calorie intake and prolonged treatment with rapamycin have been shown to extend the lifespan of animals and delay the onset of the age-related decline in tissue and organ function. Using a reporter line in which neural stem and progenitor cells are marked by the expression of green fluorescent protein (GFP), we examined the effect of prolonged exposure to calorie restriction (CR) or rapamycin on hippocampal neural stem and progenitor cell proliferation in aging mice. We showed that CR increased the number of dividing cells in the dentate gyrus of female mice. The majority of these cells corresponded to nestin-GFP-expressing neural stem or progenitor cells; however, this increased proliferative activity of stem and progenitor cells did not result in a significant increase in the number of doublecortin-positive newborn neurons. Our results suggest that restricted calorie intake may increase the number of divisions that neural stem and progenitor cells undergo in the aging brain of females.

Young and old genetically heterogeneous HET3 mice on a rapamycin diet are glucose intolerant but insulin sensitive

Rapamycin, an inhibitor of the mechanistic target of rapamycin (mTOR) signaling pathway, extends the life span of yeast, worms, flies, and mice. Interventions that promote longevity are often correlated with increased insulin sensitivity, and it therefore is surprising that chronic rapamycin treatment of mice, rats, and humans is associated with insulin resistance (J Am Soc Nephrol., 19, 2008, 1411; Diabetes, 00, 2010, 00; Science, 335, 2012, 1638). We examined the effect of dietary rapamycin treatment on glucose homeostasis and insulin resistance in the genetically heterogeneous HET3 mouse strain, a strain in which dietary rapamycin robustly extends mean and maximum life span. We find that rapamycin treatment leads to glucose intolerance in both young and old HET3 mice, but in contrast to the previously reported effect of injected rapamycin in C57BL/6 mice, HET3 mice treated with dietary rapamycin responded normally in an insulin tolerance test. To gauge the overall consequences of rapamycin treatment on average blood glucose levels, we measured HBA1c. Dietary rapamycin increased HBA1c over the first 3 weeks of treatment in young animals, but the effect was lost by 3 months, and no effect was detected in older animals. Our results demonstrate that the extended life span of HET3 mice on a rapamycin diet occurs in the absence of major changes in insulin sensitivity and highlight the importance of strain background and delivery method in testing effects of longevity interventions.

The role of mTORC1 in regulating protein synthesis and skeletal muscle mass in response to various mechanical stimuli

Skeletal muscle plays a fundamental role in mobility, disease prevention, and quality of life. Skeletal muscle mass is, in part, determined by the rates of protein synthesis, and mechanical loading is a major regulator of protein synthesis and skeletal muscle mass. The mammalian/mechanistic target of rapamycin (mTOR), found in the multi-protein complex, mTORC1, is proposed to play an essential role in the regulation of protein synthesis and skeletal muscle mass. The purpose of this review is to examine the function of mTORC1 in relation to protein synthesis and cell growth, the current evidence from rodent and human studies for the activation of mTORC1 signaling by different types of mechanical stimuli, whether mTORC1 signaling is necessary for changes in protein synthesis and skeletal muscle mass that occur in response to different types of mechanical stimuli, and the proposed molecular signaling mechanisms that may be responsible for the mechanical activation of mTORC1 signaling.

Aging-induced dysregulation of dicer1-dependent microRNA expression impairs angiogenic capacity of rat cerebromicrovascular endothelial cells

Age-related impairment of angiogenesis is likely to play a central role in cerebromicrovascular rarefaction and development of vascular cognitive impairment, but the underlying mechanisms remain elusive. To test the hypothesis that dysregulation of Dicer1 (ribonuclease III, a key enzyme of the microRNA [miRNA] machinery) impairs endothelial angiogenic capacity in aging, primary cerebromicrovascular endothelial cells (CMVECs) were isolated from young (3 months old) and aged (24 months old) Fischer 344 × Brown Norway rats. We found an age-related downregulation of Dicer1 expression both in CMVECs and in small cerebral vessels isolated from aged rats. In aged CMVECs, Dicer1 expression was increased by treatment with polyethylene glycol-catalase. Compared with young cells, aged CMVECs exhibited altered miRNA expression profile, which was associated with impaired proliferation, adhesion to vitronectin, collagen and fibronectin, cellular migration (measured by a wound-healing assay using electric cell-substrate impedance sensing technology), and impaired ability to form capillary-like structures. Overexpression of Dicer1 in aged CMVECs partially restored miRNA expression profile and significantly improved angiogenic processes. In young CMVECs, downregulation of Dicer1 (siRNA) resulted in altered miRNA expression profile associated with impaired proliferation, adhesion, migration, and tube formation, mimicking the aging phenotype. Collectively, we found that Dicer1 is essential for normal endothelial angiogenic processes, suggesting that age-related dysregulation of Dicer1-dependent miRNA expression may be a potential mechanism underlying impaired angiogenesis and cerebromicrovascular rarefaction in aging.

Circulating factors induced by caloric restriction in the nonhuman primate Macaca mulatta activate angiogenic processes in endothelial cells

Moderate caloric restriction (CR) without malnutrition increases healthspan in virtually every species studied, including nonhuman primates. In mice, CR exerts significant microvascular protective effects resulting in increased microvascular density in the heart and the brain, which likely contribute to enhanced tolerance to ischemia and improved cardiac performance and cognitive function. Yet, the underlying mechanisms by which CR confer microvascular protection remain elusive. To test the hypothesis that circulating factors triggered by CR regulate endothelial angiogenic capacity, we treated cultured human endothelial cells with sera derived from Macaca mulatta on long-term (over 10 years) CR. Cells treated with sera derived from ad-libitum-fed control monkeys served as controls. We found that factors present in CR sera upregulate vascular endothelial growth factor (VEGF) signaling and stimulate angiogenic processes, including endothelial cell proliferation and formation of capillary-like structures. Treatment with CR sera also tended to increase cellular migration (measured by a wound-healing assay using electric cell-substrate impedance sensing [ECIS] technology) and adhesion to collagen. Collectively, we find that circulating factors induced by CR promote endothelial angiogenic processes, suggesting that increased angiogenesis may be a potential mechanism by which CR improves cardiac function and prevents vascular cognitive impairment.